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Tuesday, January 20, 2009

Converting atrial fibrillation to a normal rhythm

Converting AF to a normal rhythm can be accomplished with medications (chemical cardioversion) or by electrical shocks (electrical cardioversion). Doctors usually recommend that all patients with chronic sustained AF undergo at least one attempt at cardioversion, chemical or electrical. Successful cardioversion can alleviate symptoms, improve exercise tolerance, improve quality of life, and lower the risk of strokes. Doctors usually try medical cardioversion first, and, if medications fail, then try electrical cardioversion.
Patients who are more likely to attain and maintain a normal heart rhythm with either chemical or electrical cardioversion include:
Patients younger than 65 years of age
Patients who have had AF for a short time (less than 12 months)
Patients with normal-sized atria and ventricles
Patients who are having their first episode of AF
Cardioversion with medications. Before prescribing medications for cardioversion, the doctor usually controls the rate of ventricular contractions and thins the blood, usually with warfarin. 1) Available Medications. Medications used in cardioversion usually work by blocking the channels in the walls of cells through which ions travel (sodium channels, potassium channels, beta adrenergic channels, and calcium channels). Some examples of these medications include:
quinidine (Quinaglute)
procainamide (Procan SR)
disopyramide (Norpace)
flecainide (Tambocor)
sotalol (Betapace)
flecainide (Tambocor)
amiodarone (Cordarone) These medications are capable of converting AF to normal rhythm in about 50% of patients. They often are used long-term to maintain a normal rhythm and prevent recurrences of AF. 2) Disadvantages of using medications. Medications used for converting AF carry a small risk of causing other abnormal heart rhythms--they are said to be pro-arrhythmic--especially in patients with diseases of the heart muscle or coronary arteries. These abnormal heart rhythms can be more life-threatening than AF. Therefore, treatment with these medications often is initiated in the hospital while the patient's rhythm is continuously monitored for 24-72 hours. These medications may not be effective in the longer-term. Many patients eventually develop a recurrence of AF despite the medications. Medications used in treating atrial fibrillation often have important side effects. Many patients discontinue them because they cannot tolerate these side effects. For example, amiodarone is commonly used in treating AF because it is less pro-arrhythmic and has been shown to maintain a normal rhythm in up to 75% of patients. However, amiodarone frequently causes side effects and drug interactions. About 7 out of every 10 patients taking amiodarone experience some type of side effect, and between 1 in 5 and 1 in 20 experience side effects that are severe enough that the amiodarone must be stopped. Amiodarone can interact with other medications such as tricyclic antidepressants, e.g., amitriptyline (Elavil) or phenothiazine antipsychotics, e.g., chlorpromazine (Thorazine) and cause abnormal heart rhythms. Amiodarone interacts with warfarin and increases the risk of bleeding. This interaction with warfarin can occur as early as 4-6 days after the start of both drugs or can be delayed by a few weeks. Thus, doctors prescribing both warfarin and amiodarone will adjust the dose of warfarin to avoid excessive blood thinning. Amiodarone also can cause thyroid disturbances in the fetus when administered orally to the mother during pregnancy. Amiodarone also may affect thyroid function in adults. The most severe side effect of amiodarone is lung toxicity that potentially can be fatal. Because of this lung toxicity, patients should report any symptoms of cough, fever, or painful breathing to their doctors.
Electrical cardioversion. Electrical cardioversion is a procedure used by doctors to convert an abnormal heart rhythm (such as AF) to a normal rhythm (sinus rhythm). Electrical cardioversion requires the administration of an electrical shock over the chest. This electrical shock stops the abnormal electrical activity of the heart for a brief moment and allows the normal heart rhythm to take over. Although electrical cardioversion can be used to treat almost any abnormal fast heartbeat (such as atrial flutter and ventricular tachycardia), it is used most frequently to convert AF to a normal rhythm.
Warfarin usually is given for 3 to 4 weeks prior to cardioversion to minimize the risk of stroke that can occur during or shortly after cardioversion. Warfarin is continued for four to six weeks after successful cardioversion. For some patients requiring urgent electrical cardioversion, warfarin may not work fast enough to thin the blood. Therefore, these patients may be given heparin prior to electrical cardioversion. Heparin is a faster-acting blood thinner than warfarin, but it must be administered as a continuous intravenous infusion or as injections under the skin. After successful cardioversion, these patients can be switched from heparin to warfarin.
1) Method of cardioversion. Electrical cardioversions (urgent and elective) usually are performed in a hospital. For elective (non-urgent) electrical cardioversion, patients usually arrive at the hospital without eating in the morning. Necessary medications can be taken with small sips of water. Patients are given supplemental oxygen via nasal catheters, and an intravenous infusion of fluids is started. Electrodes (pads) are placed on the skin over the chest to continuously monitor the heart rhythm. Paddles then are placed over the chest and the upper back. Patients are sedated (anesthetized) intravenously with medications. This is followed by a strong electric shock through the paddles. The shock converts the AF to a normal rhythm. After cardioversion, patients are observed for several hours or overnight to make sure that their normal heart rhythm is stable.
2) Effectiveness of electrical cardioversion. Electrical cardioversion is more effective than medications alone in terminating AF and restoring a normal heart rhythm. Electrical cardioversion successfully restores a normal heart rhythm in over 95% of patients.
3) Limitations of electrical cardioversion. While electrical cardioversion is effective in converting AF to a normal heart rhythm, the normal rhythm may not continue for long. Approximately 75% of patients successfully treated with electrical cardioversion experience a recurrence of AF within 12-24 months. Older patients with enlarged atria and ventricles who have had AF for a long time are especially prone to recurrences. Thus, most patients who undergo successful cardioversion are placed on oral medications to prevent recurrences of AF.
4) Risks of electrical cardioversion. The risks of electrical cardioversion include stroke, heart attack, burns of the skin, and in rare instances, death.
5) Candidates for electrical cardioversion. Doctors usually recommend that all patients with chronic, sustained AF undergo at least one attempt at cardioversion. Cardioversion usually is attempted with medications first. If medications fail, electrical cardioversion can be considered. Sometimes a doctor may choose to use electrical cardioversion first if AF is of short duration (onset within 48 hours) and the transesophageal echocardiography shows no blood clots in the atria.
Electrical cardioversion is performed urgently (on an emergency basis) on patients with severe and potentially life-threatening symptoms caused by AF. For example, some patients with rapid AF can develop chest pain, shortness of breath, and dizziness or fainting. (Chest pain in these patients is due to an insufficient supply of blood to the heart muscles. Shortness of breath indicates ineffective pumping of blood by the ventricles. Fainting or dizziness usually is due to dangerously low blood pressure.)
Rate control therapy. Recent studies have shown that an acceptable alternative to cardioversion (chemical or electrical) is rate-control therapy. In rate-control therapy, the doctor will leave the patients in AF provided their rate of ventricular contractions is under good control, the output of blood from the heart is adequate, and their blood is adequately thinned by warfarin to prevent strokes. Heart rate in these patients can be controlled using medications such as beta-blockers, calcium channel blockers, or digoxin or AV node ablation with pacemaker implantation. Rate-control therapy is used to simplify therapy and avoid the side effects of anti-arrhythmic medications (medications used to treat and prevent AF).
Over long periods of observation, patients treated with rate-control therapy have similar survival and quality of life as compared to patients who undergo repeated electrical or chemical cardioversions.
Suitable candidates for rate-control therapy include:
Patients who have had AF for more than one year
Patients with significant disease of the heart valves
Patients with enlarged hearts as a result of heart failure or cardiomyopathy (heart muscle weakness)
Patients with significant or intolerable side effects with medications for AF

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